1. Field of the Invention
The present invention relates to a vertical machine tool with a movable main spindle. An axis of the main spindle is directed substantially vertically to a floor surface and a headstock is movable in parallel with the axis of the main spindle. More particularly, the present invention relates to the machine tool which may perform a so-called bar feed machining in which a bar workpiece (bar work) inserted into the main spindle is repeatedly projected by a predetermined amount, is machined into a predetermined shape, is cut by a cut-off tool or a parting tool and is caused to move outside the machine tool.
2. Description of the Related Art
In many cases in a lathe with an axis of a main spindle being directed in a horizontal direction, a bar feed machining is performed. In this bar feed machining, a bar workpiece (bar member or bar work) with an axial dimension longer than a radial dimension is fed by a bar feed device and simultaneously therewith, the bar workpiece which has been subjected to the turning is cut off by a cut-off tool or the like.
However, there is a vertical machine tool, with a movable main spindle, in which a headstock is movable at least in a first direction (Z-axis direction) in parallel with an axis of the main spindle. The bar feed machining by this machine tool has many issues to be technically solved because the main spindle and the bar workpiece are directed substantially vertically to the floor surface.
Therefore, a technical approach relating a bar workpiece feed device or the like for the vertical machine tool with the movable main spindle has been proposed by, for example, Japanese Patent Laid-Open Application (Publication No. P2000-79501). This publication discloses a technology relating a bar workpiece feed device for inserting a bar workpiece from a direction of the chuck by the operation for moving the bar workpiece in a Z-axis direction (a direction in parallel with the axis of the main spindle) and by the operation for driving and raising the bar workpiece by a driver.
In case of the machine tool, with the movable main spindle, having a headstock moving in a direction (Z-axis direction) in parallel with the axis of the main spindle, the headstock on which a cut-off tool is fixed does not move in the Z-axis direction in many cases. Also, in order to prevent the generation of rattle, it is usually preferable to perform the cut-off machining by the cut-off tool in a position near to the chuck as much as possible. Further, it is preferable that a structure and an operation of a bucket for receiving the cut workpiece are simple.
FIG. 14A and FIG. 14B are illustrations of the operation for cutting the bar workpiece 6 by a conventional vertical machine tool 200 with a movable main spindle.
As shown in FIG. 14A and FIG. 14B, in case of the machine tool 200, a headstock 202 moves up and down relative to a cut-off tool 201. Then, an axial dimension of the machined workpiece 6a is set at predetermined dimensions “L1” and “L2”.
The bar workpiece 6 is cut by the cut-off tool 201 so that the cut workpiece 6a is received in a bucket 203. In this case, the shorter the distance “h1” and “h2” between a lower end of the machined workpiece 6a and a bottom surface of the bucket 203, the less the damage will become and the better the operation for receiving the workpiece 6a will become when the machined workpiece 6a drops.
On the other hand, the bar workpiece 6 inserted into the main spindle is gripped at one end by the chuck (or collet chuck). However, unless another position away from the chuck at a predetermined distance is held, the bar workpiece 6 makes a so-called gyro motion due to the rotation of the main spindle to generate vibration and to cause the degradation in precision.
Accordingly, in the lathe of which the main spindle is directed horizontally, the gyro motion is prevented by inserting a filler tube into the main spindle.
There is a machine tool having a structure in which a bucket 203 shown in FIG. 14A and FIG. 14B only makes a swinging motion between a receiving position, at which the machined workpiece 6a is received, and a discharging position, from which the machined workpiece 6a is discharged, thereby moving the machined workpiece 6a. In this case, a level of the bucket 203 in the receiving position is always kept constant.
Therefore, as shown in FIG. 14A, in order to make suitable a distance “h1” between a lower end of the machined workpiece 6a and a bottom surface of the bucket 203, a height of the bucket 203 is set by setting an axial dimension of the machined workpiece 6a in conformity with the maximum length “L1”. However, if such a setting is taken, in case of the machined workpiece 6a having a short axial dimension “L2” as shown in FIG. 14B, a distance “h2” between the lower end of the machined workpiece 6a and the bottom surface of the bucket 203 is increased.
Thus, if the distance “h2” is long, there is a fear that the machined workpiece 6a would be damaged when the machined workpiece 6a drops down to the bucket 203. Therefore, there is a demand that this point should be solved.
Japanese Patent Laid-Open Application (Publication No. 11-10407) discloses a workpiece discharge device. A machine tool provided with this workpiece discharge device is a lathe in which an axis of a main spindle is directed in a horizontal direction.
In the workpiece discharge device described in the patent publication (No. 11-10407), a preparation position in which the machined workpiece cut away from a bar member is received in the bucket for the workpiece is adjustable, accordingly the construction becomes complicated.
Also, if the adjustable range is to be increased, when the bucket is swung to the front cover covering the front side of the machining area, the bucket is not identified with the position of a discharge chute formed in a front cover. As a result, there is a fear that the machined workpiece might not be smoothly transferred from the bucket to the chute, so that the adjustable range could not be increased.
On the other hand, in the case where a diameter of the workpiece is changed, filler tubes for preventing the gyro motion of the workpiece should be replaced for setup. However, in the vertical machine tool with the movable main spindle, it is very troublesome to perform the setup change of the filler tubes and the like.
It is therefore expected to provide a vertical machine tool, with a movable main spindle, which may perform the bar feed machining while preventing the gyro motion of the bar workpiece without setup changing operation such as the filler tube changing operation.
In some cases, the bar feed device is attached to a lathe in which the axis of the main spindle is directed in the horizontal direction. In those cases, the bar feed device having the installation area corresponding to the length of the bar workpiece should be arranged on a rear portion of the main spindle. Therefore, there is a problem that the installation area of the lathe would be considerably increased.